Adsorbents for removal of mercury vapor from air or gas

ABSTRACT

Adsorbents for removal of mercury vapor from air or gas including activated carbon granules impregnated with interhalogen compounds, particularly iodine monochloride and iodine trichloride.

United States Patent Revoir et al.

[ 1 May 16, 1972 [54] ADSORBENTS FOR REMOVAL OF MERCURY VAPOR FROM AIROR GAS [72] Inventors: William H. Revoir, West Hartford, Conn;

John A. Jones, Springfield, Mass.

[56] References Cited UNITED STATES PATENTS 1,984,164 12/1934 Stock..252/441 Primary Examiner-Charles N. l-lart Attorney-William C. Nealon,Noble S. Williams, Robert J. Bird and Bernard Sweeney [57] ABSTRACTAdsorbents for removal of mercury vapor from air or gas includingactivated carbon granules impregnated with interhalogen compounds,particularly iodine monochloride and iodine trichloride.

2 Claims, 3 Drawing Figures PATENTEDMAY 16 I972 3,662,523

SHEET 1 OF 2 weught Increase of carbon vanuhon of -|ncreuse m welghfofcarbon due to lmpregnahon by lodme monochlorlde and lodme trlchlorldewlth tlme of lmpregncmon lmpregnaflon wlih ICI 20 40 .60 80 I00 I20 I40I60 lmpregnuflon flme (mlnutes) lnmal welght of each carbon batch I 200grams tempermure of lmpregnahonl 40 C on flow rate: l0 LPM INVENTOR.Willem H. Revolr ATTO NEY FIG. 2

ADSORBENTS FOR REMOVAL OF MERCURY VAPOR FROM AIR R GAS BACKGROUND OF THEINVENTION The present invention relates in general to adsorbentmaterials and more particularly to adsorbent materials for the removalof toxic mercury vapor from air or gasses.

In the prior art, the best adsorbent we knew of for mercury vapor is acomposition of activated carbon granules impregnated with the iodine.The iodine impregnant in activated carbon granules reacts with mercuryvapor to yield the solid mercuric iodide which remains in the carbongranules. Respirator filters and canisters in present usage generallycontain this active ingredient for protection against mercury vapors.

SUMMARY OF THE INVENTION It is an object of the present invention toprovide an adsorbent material for mercury vapor of improvedeffectiveness which will permit a longer useful life for a given sizefilter element, or conversely permit a smaller size filter element for agiven useful life.

These objects are realized by an adsorbent material for mercury vaporincluding a composition of activated carbon granules impregnated withiodine monochloride. In another form, the activated carbon granules areimpregnated with iodine trichloride.

DRAWING FIG. 1 is a diagram of an apparatus for the impregnation ofcarbon granules with iodine chloride or iodine trichloride.

FIG. 2 is a curve of weight increase of carbon vs. time of impregnationwith adsorbent.

FIG. 3 is a comparison chart showing the relative effectiveness offilters containing equal amounts, by weight, of adsorbent.

DESCRIPTION In general, the composition of this invention includesactivated carbon granules impregnated with an interhalogen compound foruse as an adsorbent material for mercury vapor. In particular, twointerhalogen compounds are presently preferred. These are iodinemonochloride and iodine trichloride. While both are suitable and both agreat improvement over iodine, for purposes of Rule 7 lb, iodinetrichloride adsorbent is presently contemplated as the best mode ofcarrying out this invention. However, other factors than chemicalreaction with mercury might effect this preference. These compoundsreact with mercury to produce mercuric iodide and mercuric chloride,non-volatile solids.

The reaction of vaporous mercury and iodine (prior art) is representedby the equation:

The reaction of vaporous mercury. and iodine monochloride is representedby the equation:

2Hg 2l Cl Hg C1 Hg I The reaction of vaporous mercury and iodinetrichloride is represented by the equation:

4Hg 2I C1 3Hg Cl, Hg I Referring now to FIG. 1, a laboratory apparatusis shown in which carbon granules are impregnated with iodinemonochloride or iodine trichloride. In this apparatus, generally,indicated at 2, is included a flask 4 containing activated carbongranules 22 and operatively connected to a mechanical vibrator 6. Aflask 8 contains the liquid iodine monochloride 20 (or iodinetrichloride). A heating element 10 surrounds flask 8. Flasks 4 and 8 aresuitably capped by stoppers 12, each having two appertures for thepassage of tubing. An air line 14 which is covered with a heating tape24 introduces controlled air at a positive pressure and at an elevatedtemperature to flask 8. Vapor line 16, which is covered with thermalinsulation material, connects flasks 4 and 8, and exhaust line 18 leadsfrom flask 4 to atmosphere.

Iodine monochloride (or iodine trichloride) is heated in flask 8. Airfrom line 14 drives the resulting vapor from flask 8 through vapor line16 into a bed of granulated carbon 22 in flask 4. The granulated carbonis agitated so as to provide an even distribution of the vapor throughthe granules. This vapor is continually adsorbed in the carbon until adesired weight increase is achieved. For purposes of this experiment, a15 percent weight increase has been used as the standard for comparison.Thus, identical samples of granulated carbon are impregnatedrespectively with a desired weight increase of iodine monochloride andiodine trichloride.

FIG. 2 is representative of weight increase-time relationship, showingthatthe weight increase of the carbon is substantially linear withrespect to time of impregnation. The separate curves represent theimpregnation timeswith iodine monochloride and iodine trichloride, asshown.

FIG. 3 is a plot of mercury vapor concentration in a filter exhaust,relative to the time duration of the passage of such vapor through afilter. The dashed line on this graph represents a safety thresholdlevel. Curves A, B, C represent the data for filters containing equalweight percentages (15 percent) of iodine, iodine monochloride, andiodine trichloride, respectively. The amounts of activated carbon arethe same in each case. From this graph, it will be apparent that thebreathing threshold limit level in this experiment was reached atapproximately I 400 minutes with iodine, 800 minutes with iodinemonochloride, and 1,600 minutes with iodine trichloride.

From the foregoing equations, it is apparent that equal numbers ofiodine and iodine monochloride molecules react with equal numbers ofmercury atoms. Thus, if the reactions were allowed to go to completion,(the filters exhausted) equal numbers of adsorbent molecules of iodineor iodine monochloride would react with the same quantity of mercury.However, due to the nature of the use of this invention, reactions donot go to completion. As an illustration, vapor containing ppm mercuryis passed through a filter until the effluent contains l ppm mercury. Ifthe adsorbent were allowed to completely react, the vapor would'bepassed through the filter until the effluent contained the same mercuryconcentration as the input vapor).

The pronounced improvement in the efficiency of the interhalogens asmercury adsorbents, as compared to iodine, is partially accounted for bythe fact that interhalogen compounds are more reactive than individualhalogens. The combination of halogens in inter-halogen compoundsproduces a synergistic effect.

Other interhalogen compounds could be used to produce the enhancedadsorbtion effect on mercury. They are not presently preferred for thisuse, however, primarily because of economic, not chemicalconsiderations. Examples of such compounds are:

Cl F Cl F Br F Br F Br F IF IF IF It will be apparent that an adsorbentmaterial of activated carbon granules impregnated with'iodinemonochloride or iodine trichloride has greater efiectiveness than theprior art material of activated carbon granules impregnated with iodine.Thus, by the use of this invention, greater capacity mercury vaporfilters can be provided of a given size, or conversely smaller filtersof a given capacity are made possible. Such filters may be used onrespirators to protect personnel against inhalation of mercury vapor oron large industrial processing equipment containing mercury to preventcontamination of the atmosphere with mercury vapor.

What is claimed is:

1. An adsorbent material for the removal of mercury vapor from gas, saidmaterial including activated carbon granules impregnated with aninterhalogen compound.

2. A gas filter element containing an active material for the adsorptionof mercury vapor as defined in claim 1.

2. A gas filter element containing an active material for the adsorptionof mercury vapor as defined in claim 1.